1. Technical Field
The present invention relates to a liquid crystal display device and particularly to a liquid crystal display device in which a plurality of electrostatic protecting switching elements is formed in each of dummy pixels formed in the circumference of a display area.
2. Related Art
In general, a liquid crystal display device has features of thinness, lightweight and lower power consumption. In particular, an active matrix mode liquid crystal display device using thin film transistors (TFTs) as a switching element has been widely used in a mobile phone, a portable terminal, a large-scale TV, etc. However, in the liquid crystal display device, a display defect occurs in a step of finishing the liquid crystal display device, when static electricity invades a display area during a manufacturing process or during use time. In particular, it is easy for electrostatic defect to occur with high precision in a medium or small sized device. The static electricity may be also generated due to contact with another device, even when a panel is transported in the manufacturing process. Moreover, the static electricity is most frequently generated by rubbing, when an alignment film is rubbed. Accordingly, in a technique for manufacturing the liquid crystal display device, a request has been made to prevent a display defect from occurring due to the static electricity.
In order to prevent a display defect from occurring due to the static electricity, JP-A-2006-276590 discloses a liquid crystal display device in which dummy pixels are formed in the circumference of a display area and a plurality of electrostatic protecting minute dummy pixel electrodes and switching elements are formed within the dummy pixel. Here, the configuration of a dummy pixel area of the liquid crystal display device disclosed in JP-A-2006-276590 will be described with reference to FIGS. 12 to 14.
FIG. 12 is an enlarged plan view illustrating a dummy pixel area of an array substrate disclosed in JP-A-2006-276590. FIG. 13 is an enlarged plan view illustrating the region XIII of FIG. 12. FIG. 14 is a sectional view taken along the line XIV-XIV of FIG. 13.
A known liquid crystal display device 50 is a transflective liquid crystal display device in which a plurality of scanning lines and a plurality of signal lines are formed in a matrix shape on a first light-transmitting substrate 51 with a gate insulating film interposed therebetween. In FIG. 12, only scanning lines Xn−2, Xn−1, Xn, Xn+1, and Xn+2 and signal lines Y1, Y2, . . . , and Ym are illustrated. Areas surrounded by a plurality of scanning lines X1, X2, . . . , and Xn and the plurality of signal lines Y1, Y2, . . . , and Ym are display areas. Area surrounded by the plurality of scanning lines Xn, Xn+1, and Xn+2 and the plurality of signal lines Y1, Y2, . . . , and Ym are non-display areas.
In the display area, a pixel electrode 52 and a reflection plate 65 contributing to a display are formed in each of areas surrounded by the scanning lines and the signal lines. In TFTs 54, each of source electrodes S is connected to each of the signal lines Y1, Y2, . . . , and Ym, each of gate electrodes G is connected to each of the scanning lines X1, X2, . . . , and Xn, and each of drain electrodes D is electrically connected to each of the pixel electrodes 52 and each of the reflection plates 65 with a contact hole (not shown) interposed therebetween. An auxiliary capacitor electrode 53 is provided in the lower portion of the drain electrode D. Since an operational principle of the liquid crystal display device 50 having such a configuration is known, the detailed description is omitted.
On the other hand, the non-display areas surrounded by the plurality of scanning lines Xn, Xn+1, and Xn+2 and the plurality of signal lines Y1, Y2, . . . , and Ym are formed in the periphery of the display areas of the liquid crystal display device 50. In each of the non-display areas, a plurality of dummy pixels including a TFT 66 and a dummy pixel electrode 67 which does not contribute to a display are formed in each of the signal lines Y1, Y2, . . . , and Ym. In the TFTs 66 of the dummy pixels, each of source electrodes S is connected in parallel to each of the signal lines Y1, Y2, . . . , and Ym, each of gate electrodes G is connected in parallel to each of the scanning lines Xn+1 and Xn+2, and each of drain electrodes D is connected to each of the dummy pixel electrodes 67 formed on an inter-layer film 69 with a contact hole 68 interposed therebetween, as shown in FIG. 14. In addition, the TFT 66 of the dummy pixel is formed so as to be smaller than the channel width and the channel length of a TFT 64 connected to the pixel electrode 52 contributing to a display. Therefore, the TFT 66 is subjected to electrostatic breakdown earlier than the TFT 54 connected to the pixel electrode 52 contributing to a display.
The area of the dummy pixel electrode 67 is smaller than the sum of the areas of the reflection plate 65 and the pixel electrode 52 contributing to a display corresponding to one pixel in the display area. In FIGS. 12 and 13, the area of the dummy pixel electrode 67 is 1/10 of the sum of the areas of the reflection plate 65 and the pixel electrode 52 contributing to a display corresponding to one pixel in the display area. Ten dummy pixel electrodes are provided between the scanning lines Xn and Xn+1 and between the scanning lines Xn+1 and Xn+2, respectively. That is, a total of twenty dummy pixel electrodes are provided.
In the liquid crystal display device 50 having such a configuration, when static electricity invades from a signal line input terminal 62, a TFT661 located in a dummy pixel area and nearest to the signal line input terminal 62 is subjected to electrostatic breakdown and discharges the static electricity. Thereafter, when static electricity again invades from the signal line input terminal 62, a TFT662 next to the TFT661 located in the dummy pixel area and earlier subjected to the electrostatic breakdown is subjected to the electrostatic breakdown and discharges the static electricity. Accordingly, since the invasion of the static electricity resulting in the breakdown of the thin film transistor 54 located in the display area can be allowed up to twenty times during the manufacture of the liquid crystal display device 50, it is possible to obtain the transflective liquid crystal display device 50 which actually has no display defect.
However, the dummy pixels of the liquid crystal display device 50 disclosed in JP-A-2006-276590 are formed in the non-display areas (hereinafter, referred to as “a source dummy pixel area”) on the upper and lower sides of the display areas in a plan view. Therefore, since the plurality of dummy pixels is formed within an area corresponding to one pixel in the source dummy pixel area, it is possible to cope with the plural invasions of the static electricity from the signal line. However, in the non-display areas (hereinafter, referred to as “a gate dummy pixel area”) on the right and left sides of the display area in a plan view, it is difficult to form the plurality of dummy pixels in an area corresponding to one pixel. Therefore, in order to cope with the plural invasions of the static electricity from a side of the scanning lines, the plurality of dummy pixels have to be formed on both the right and left sides of the display areas in a plan view toward the outside. For this reason, it is difficult to narrow the width of the gate dummy pixel area. Moreover, since the dummy pixels of the liquid crystal display device 50 disclosed in JP-A-2006-276590 each include the TFT 66 and the dummy pixel electrode 67, the configuration is complicated.